Plunger-type measuring pump

ABSTRACT

A plunger-type measuring pump in which a pump head  9  can be correctly attached to a pump body  1  with a reduced amount of time and labor is provided. The plunger-type measuring pump according to the present invention includes: a pump body  1  supporting a plunger  2  while allowing a reciprocating motion of the plunger  2;  a cylindrical head-attachment portion  82  provided at one end of the pump body  1,  the head-attachment portion  82  having a male-thread portion  83  formed on an outer circumference thereof; a pump head  9  having a pump chamber  91  inside, the pump head  9  being designed to be attached to the head-attachment portion  82  with a seal  4  therebetween; and a sleeve-like fixing part  7  to be fitted onto the outer circumference of the pump head  9,  the sleeve-like fixing part  7  having an inner circumferential wall on which an engaging portion  74  to be engaged with the pump head  9  and a female-thread portion  72  to be screwed onto the male-thread portion  83  are formed. Since a single sleeve-like fixing part  7  is used to fix the pump head  9  to the cylindrical head-attachment portion  82  provided on the pump body  1,  it is unnecessary to pay attention to the evenness in the tightening force applied to bolts  6.

TECHNICAL FIELD

The present invention relates to a plunger-type measuring pump formeasuring out and sending an amount of liquid by driving a plunger intoa reciprocating motion

BACKGROUND ART

Plunger-type measuring pumps are widely used as a mechanism formeasuring out an amount of liquid and sending it to an analyticalinstrument or other systems. A plunger-type measuring pump is a devicein which a plunger is reciprocated in a pump chamber to continuouslyfeed a constant amount of liquid.

FIG. 1 is an exploded perspective view of a conventional type ofplunger-type pump, and FIG. 2 is a sectional view of the same pump. Thisplunger-type pump has a pump body 1, a plunger 2, a pump head 3, aplunger seal 4 with a seal holder 5, two bolts 6 for fixing the pumphead 3 to the pump body 1, and other elements. The pump head 3 has aninternal pump chamber 31 with a liquid suction port 32 for suckingliquid into the pump chamber 31 and a liquid discharge port 33 fordischarging liquid from the pump chamber 31. The plunger seal 4, whichis held by the seal holder 5, maintains the liquid-tightness of the pumpchamber 31.

When the plunger 2 is reciprocated in the pump chamber 31, a specifiedconstant amount of liquid is sucked through the suction port 32 into thepump chamber 31 and sent to an analytical instrument or other systems.

BACKGROUND ART DOCUMENT Patent Document

Patent Document 1: JP-A 10-103221

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In this conventional plunger-type measuring pump, the pump head 3 isattached to the pump body 1 with a plurality of fixing parts 6, such asbolts. If these bolts are unevenly tightened, the pump head 3 attachedto the pump body 1 will be inclined, causing an uneven force on theplunger seal 4, which results in a deformation of the plunger seal 4.The deformation of the plunger seal 4 leads to the leakage of liquidfrom the pump chamber 31, the breakage of the plunger seal 4 and theshortening of its life.

The aforementioned problems can be avoided by evenly tightening thebolts 6. However, it requires a skilled technician to meticulouslytighten the bolts 6. Thus, a considerable amount of time and labor isneeded to attach the pump head 3.

The present invention has been developed in view of the aforementionedproblem, and its objective is to reduce the time and labor for correctlyattaching the pump head to the pump body.

Means for Solving the Problems

In a plunger-type measuring pump for sending liquid by reciprocating aplunger in a pump chamber, the plunger-type measuring pump according tothe present invention is characterized by including:

a pump body for supporting the plunger while allowing a reciprocatingmotion of the plunger;

a cylindrical head-attachment portion provided at one end of the pumpbody, the head-attachment portion having a male-thread portion on anouter circumference thereof;

a pump head having the pump chamber inside, the pump head being designedto be attached to the head-attachment portion with a seal therebetween;and

a sleeve-like fixing part to be fitted onto the outer circumference ofthe pump head, the sleeve-like fixing part having an innercircumferential wall on which an engaging portion to be engaged with thepump head and a female-thread portion to be screwed onto the male-threadportion are formed.

In one mode of the aforementioned plunger-type measuring pump, the pumphead has a flange with which the engaging portion is to be engaged.

In another mode of the aforementioned plunger-type measuring pump, thesleeve-like fixing part has a large-hole section having a large innerdiameter and a small-hole section having a small inner diameter, and theengaging portion is a boundary section between the large-hole sectionand the small-hole section.

Effects of the Invention

In the plunger-type measuring pump according to the present invention, asingle sleeve-like fixing part is used to fix the pump head to thecylindrical head-attachment portion provided on the pump body. Unlikethe conventional case where a plurality of bolts are used to fix thepump head, it is unnecessary to pay attention to the evenness of thetightening force.

The pump head is attached to the pump body by screwing the female threadformed on the inner circumferential surface of the sleeve-like fixingpart on the male thread formed on the outer circumferential surface ofthe head-attachment portion. Accordingly, there is no need to use anytool in the attaching work, and the pump head can be correctly attachedwith a small amount of time and labor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a conventional plunger-typemeasuring pump.

FIG. 2 is a partial sectional view of the conventional plunger-typemeasuring pump.

FIG. 3 is an exploded perspective view of a plunger-type measuring pumpaccording to one embodiment of the present invention.

FIG. 4 is a partial sectional view of the plunger-type measuring pumpaccording to the embodiment of the present invention.

FIG. 5 is a perspective view of the fixing part according to theembodiment of the present invention.

FIG. 6 is a partial sectional view of the plunger-type measuring pumpaccording to the first variation of the present invention.

FIG. 7 is a partial sectional view of the plunger-type measuring pumpaccording to the second variation of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of the present invention is hereinafter described bymeans of FIGS. 3-5.

Embodiment

FIG. 3 is an exploded perspective view of the plunger-type measuringpump according to the present embodiment, FIG. 4 is a sectional view ofthe same pump, and FIG. 5 is a perspective view of the fixing partaccording to the present embodiment.

A major difference between the plunger-type measuring pump of thepresent embodiment and the conventional example exists in that thepresent pump uses a single fixing part 7 to fix the pump head 9 to thepump body 1.

More specifically, a projection 8 is integrally formed at one end of thepomp body 1. The projection 8 has a cylindrical section 81 and alarge-diameter section 82 whose outer diameter is larger than that ofthe cylindrical section 81. The large-diameter section 82 is provided atthe anterior end of the cylindrical section 81. A male-thread groove 83is formed on the outer circumference of the large-diameter section 82. Adepression for receiving a cylindrical seal holder 5 is formed on theside of the projection 8 facing the pump head 9. The plunger 2 issupported by the pomp body 1 in such a manner that it can reciprocate.The tip of the plunger 2 protrudes from the projection 8.

The pump head 9 has a cylindrical body having a flange 94 at one end.The outer diameter of this flange 94 is approximately equal to that ofthe large-diameter section 82 of the cylindrical section 8. A depressionfor receiving the seal holder 5 and a pump chamber 91 are formed insidethe pump head 9. Furthermore, the pump head 9 has a liquid suction port92 for sucking liquid into the pump chamber 91 and a liquid dischargeport 93 for discharging liquid from the pump chamber 91.

The seal holder 5 is a cylindrical part having a through hole 51extending in the axial direction, with a seal 4 being held on the sideof the seal holder 5 facing the pump head 9. The seal 4 has a convexshape with the projecting side facing the pump body 1.

The fixing part 7 has a nut-like shape with a through hole at itscenter. This through hole is divided into a large-hole section 71 havinga large inner diameter and a small-hole section 73 having a small innerdiameter. The inner diameter of the large-hole section 71 is slightlylarger than the outer diameter of the large-diameter section 82. Afemale-thread groove 72, which is designed to be screwed onto theaforementioned male-thread groove 83, is formed on the innercircumferential wall of the large-hole section 71. The thickness of thelarge-hole section 71 at a portion where no female-thread groove 72 isformed is slightly larger than that of the flange 94 of the pump head 9.The inner diameter of the small-hole section 73 is slightly larger thanthe outer diameter of the pump head 9.

To facilitate the tightening of the fixing part 7, four flat faces areformed on the outer circumference of the fixing part 7. The fixing part7 is made of resin and produced as a single-piece part.

In the measuring pump 10 of the present embodiment, the pump head 9 isattached to the pump body 1 as follows: Initially, the seal holder 5 isfitted into the depression of the projection 8 of the pump body 1, withthe tip of the plunger 2 being inserted into the through hole 51 of theseal holder 5. Next, the pump head 9 is attached. More specifically, theplunger 2 protruding from the seal holder 5 is fitted into the pumpchamber 91 of the pump head 9 and the seal holder 5 is fitted into thedepression of the pump head 9 so that the flange 94 comes in contactwith the end face of the large-diameter section 82.

Subsequently, the fixing part 7 is put on the pump head 9 from theanterior side and screwed to make the female-thread groove 72 engagedwith the male-thread groove 83 of the large-diameter section 82. In thisprocess, the step-like portion at the boundary of the large-hole section71 and the small-hole section 73 (this portion is hereinafter called the“step section 74”) comes in contact with the flange 94 of the pump head9. The fixing part 7 is strongly tightened until the flange 94 ispressed on the large-diameter section 82. As a result, the pump head isstrongly fixed to the projection.

In this manner, the pump head 9 is attached to the pump body 1 with asingle fixing part 7. Accordingly, it is possible to correctly attachthe pump head 9 to the pump body 1 even without taking account of thebalance of the tightening force of the fixing part. The force acting onthe plunger seal 4 also becomes uniform, so that no deformation of theplunger seal 4 will occur.

The tightening of the fixing part 7 requires no expert skills or specialtools. Therefore, the pump head 9 can be easily attached by hand work.Thus, the amount of time and labor for the attaching work is reduced.

Such an effect is particularly profitable when the plunger 2 has a largediameter (e.g. 6 mm or greater). Increasing the diameter of the plunger2 requires a corresponding increase in the size of the plunger seal 4and the pump head 9, causing the effect of an inclination of the pumphead 9 to be more noticeable and the deformation of the plunger seal 4to be more likely to occur.

The fixing part 7 can be used to fix the pump head 9 to the projection 8even if the flange 94 is thinner than the portion of the large-holesection 71 where no female thread 72 is formed. Even in this case, thepump head 9 can be fixed to the projection 8 since the fixing part 7 canbe screwed until the step section 74 comes in contact with the flange 94(see FIG. 6).

The fixing part 7 is also applicable to a pump head 9 having a flange 94whose outer diameter is smaller than that of the large-diameter section82. Even in this case, the pump head 9 can be fixed to the projection 8since the fixing part 7 can be screwed until a portion of the stepportion 74 comes in contact with the flange 94 (see FIG. 7).

Thus, according to the present invention, a fixing part 7 of the samesize can be commonly used even if the dimensions of the flange areslightly different.

Thus far, one mode for carrying out the present invention has beendescribed by means of the embodiment and variations. It should be notedthat the present invention is not limited to the previous examples; theycan be appropriately changed within the spirit of the present invention.For example, the projection 8 of the pump body 1 may have the sameexternal dimensions at every portion. The pump head 9 does not need tobe cylindrical in its entirety; the minimal requirement is that theportion of the pump head 9 to be fixed with the fixing part 7 (i.e. theportion facing the pump body 1) is cylindrical. In this case, theanterior portion of the pump head 9 must have an appropriate size sothat the fixing part 7 can be fitted on that portion.

EXPLANATION OF NUMERALS

-   1 . . . Pump Body-   2 . . . Plunger-   3 . . . Pump Head-   4 . . . Plunger Seal-   5 . . . Seal Holder-   6 . . . Bolt-   7 . . . Fixing Part-   8 . . . Projection-   9 . . . Pump Head-   31 . . . Pump Chamber-   32 . . . Liquid Suction Port-   33 . . . Liquid Discharge Port-   51 . . . Through Hole-   71 . . . Large-Hole Section-   72 . . . Female-Thread-   73 . . . Small-Hole Section-   74 . . . Boundary Phase-   81 . . . Cylindrical Section-   82 . . . Large-Diameter Section-   83 . . . Male-Thread-   91 . . . Pump Chamber-   92 . . . Liquid Suction Port-   93 . . . Liquid Discharge Port-   94 . . . Flange

1. A plunger-type measuring pump for sending liquid by reciprocating aplunger in a pump chamber, comprising: a pump body for supporting theplunger while allowing a reciprocating motion of the plunger; acylindrical head-attachment portion provided at one end of the pumpbody, the head-attachment portion having a thread portion on an outercircumference thereof; a pump head having the pump chamber inside, thepump head being designed to be attached to the head-attachment portionwith a seal therebetween; and a sleeve-like fixing part to be fittedonto the outer circumference of the pump head, the sleeve-like fixingpart having an inner circumferential wall on which an engaging portionto be engaged with the pump head and a thread portion to be screwed ontothe thread portion of the cylindrical head-attachment portion areformed.
 2. The plunger-type measuring pump according to claim 1, whereinthe pump head has a flange with which the engaging portion is to beengaged.
 3. The plunger-type measuring pump according to claim 1,wherein: the sleeve-like fixing part has a large-hole section having alarge inner diameter and a small-hole section having a small innerdiameter; and the engaging portion is a boundary section between thelarge-hole section and the small-hole section.
 4. The plunger-typemeasuring pump according to claim 2, wherein: the sleeve-like fixingpart has a large-hole section having a large inner diameter and asmall-hole section having a small inner diameter; and the engagingportion is a boundary section between the large-hole section and thesmall-hole section.